Thank you for the replies. It is not as bad as I described it, however very often it does not work. The dictionary (I tried several) is not corrupted, just looking up usually works fine. I have not yet figured out what factors influence whether it works or not. Maybe I will make a video of the malfunction. The device seems mainly to have struggles handling the switching between document and dictionary.
Among others it's this dictionary:
http://www.mobipocket.com/en/eBooks/...?BookID=127312